1. Field of the Invention
The invention relates to battery powered computer systems, and more particularly, to circuits and methods for reducing the power consumption of the computer system.
2. Description of the Prior Art
Portable computer systems are rapidly developing the capabilities of conventional desktop or floor mounted personal computer systems. Hard disk units are being integrated into portable computers because of the large amounts of information being processed and the large size of many applications programs. At east one floppy disk unit is integrated in the vast majority of portable computers, even if a hard disk unit is installed, to allow loading of information and use of applications requiring key disks and of diagnostic programs. Modems have been integrated into portable computers for some time to allow communications and information transfer between the user and a remote location, for example, the home office. The displays in the portable computer systems are becoming much more elaborate and readable. The pixel count on the standard liquid crystal displays (LCD's) utilized is increasing, as is the viewing angle. The use of backlighting allows use of LCD's in low light environments and improves the contrast ratio of the display. More complex circuitry is being installed in the portable computers to support these improved peripheral devices and to support the increased speeds and capabilities of the microprocessors utilized in the portable computer systems.
The various peripheral devices and high speed circuitry mentioned above consume large amounts of power when operating. This has made it very difficult to provide all the possible functionality available and yet have an acceptable battery life when the portable computer system is battery powered, so that it can be used in locations where alternating current is not available. Using CMOS components helped reduce the power consumption of the circuitry, but even the use of CMOS components is insufficient at the clock speeds and performance levels of available circuitry. Therefore, a dilemma arises whether to provide lesser functionality with longer battery life or greater functionality with lesser battery life or even no battery operation.
Various alternatives were tried to resolve the problem. For example, the IBM Corporation PC Convertible included a switch which the user could press to place the computer system in a standby mode, but the PC convertible with relatively simple, with a low level of functionality as compared to what is currently available and the requirement of a user action limited its use to circumstances where the user remembered to depress the switch. Blanking the display after a period of keyboard inactivity saved power as well as prolonged the life of the display and was widely utilized. A hard disk unit was developed which reduced the power used by the controlling electronics by utilizing only certain portions of the track for servo information and turning off the read channel circuitry until just before a servo burst was expected. Additionally, a programmable value could be provided to the hard disk unit so that after a given inactivity interval defined by this value, the hard disk unit was allowed to spin down and all but some interface circuitry was shut down. While these alternatives did provide some relief, they were not complete solutions to satisfactorily resolve the dilemma and design tradeoffs still were forced to occur.